JPH0766220B2 - Toner transfer device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner image transfer device that can be used in a hard copy device such as a copying machine or a printer.

2. Description of the Related Art At present, in an electrophotographic apparatus which is widely used in a copying machine or a laser printer, a toner charged after an electrostatic latent image is written on an electrostatic latent image holding member such as an electrophotographic photosensitive member. A method is well known in which a toner image is obtained on the plain paper by electrostatically adhering and developing the toner and then performing corona transfer to the plain paper using a corona charger to which a voltage having a polarity opposite to that of the toner is applied.

Problems to be Solved by the Invention In such a corona transfer method, it is known that when a plain paper absorbs moisture in the air in a high humidity environment, a toner image transfer failure occurs.

The reason for this is as follows. That is, since plain paper is mainly made of cellulose, it is an insulator under normal environment, but when the environmental humidity exceeds 70%, the moisture absorption exceeds 12%, and its resistance value is in the semiconductor region.
It was found to be reduced to 10 ¹² cm or less. When corona transfer is performed from the back surface of the paper in such a state, as shown in FIG. 2, the transfer corona charge 2 generated by the corona charger 1 which is a transfer device passes through the transfer paper 3 and the toner on the photoconductor 4 is transferred. 5
It was found that the toner was reversed to the initial charging polarity from the initial charging polarity, and the transfer failure occurred because the toner was not electrostatically pulled by the paper. In such a case, it was found that if the voltage applied to the transfer corona is set low enough to prevent the corona charge from leaking through the paper, it is possible to transfer well even with hygroscopic paper, but under such low corona voltage setting conditions. On the contrary, it was found that a transfer failure occurs due to insufficient transfer voltage during drying.

In view of the above points, the present invention is a toner transfer device capable of consistently and satisfactorily transferring a device for corona-transferring a toner image recorded on an electrostatic image carrier regardless of the degree of moisture absorption of paper. The purpose is to provide.

Means for Solving the Problems The present invention relates to a transfer device that corona-transfers a toner image onto a transfer paper by providing a corona charger at a position opposite to an electrostatic image holding member carrying a toner image. A conductive electrode to which a voltage having a polarity opposite to the polarity of the corona transfer is applied is arranged on the upstream side of the corona charger at a position where the paper is in the path of plunging into the counter position and is in contact with the transfer paper. It is a toner transfer device.

Function As mentioned above, when corona transfer is performed from the back surface of plain paper at high humidity, the paper absorbs moisture in the air and the resistance decreases, and the transfer charge amount in the paper becomes excessive than the appropriate amount, Even the toner on the photoconductor leaks and the polarity of the toner is reversed. At this time, if a conductive electrode is brought into contact with a part of the paper and a voltage with a polarity opposite to that of corona transfer is applied to this conductive electrode, it is possible to reverse that the resistance value of the paper itself changes depending on the environment. Can be used for good transfer at high humidity.

That is, as shown in FIGS. 3 (a) and 3 (b), when the conductive electrode 7 is brought into contact with the surface of the paper 6 and a voltage having a polarity opposite to that of the transfer corona is applied to the conductive electrode 7, Since the resistance of the transfer paper 6 decreases at the time of humidity, it is possible to prevent excess charges at the transfer position from being drawn into the conductive electrode 7 through the transfer paper 6 and leaking to the photoconductor 8 side through the paper 6. You can

On the other hand, when the transfer paper 6 does not absorb moisture when it is dried, the resistance of the paper becomes high. Therefore, even if a voltage is applied to the conductive electrode 7, electric charges do not flow inside the transfer paper 6, and this conductive electrode 6 does not flow. The voltage application by means does not affect the transfer performance. In other words, if the transfer corona condition is set according to the condition of the paper when it is dry, the resistance of the paper will decrease at high humidity and the effect of the conductive electrode will automatically appear, and the transfer condition will be optimized for the condition at high humidity. it can. Therefore, it is possible to obtain a transfer device which does not require any special humidity sensor or switch and automatically optimizes transfer conditions during dry and high humidity.

Further, as shown in FIG. 4, when this conductive electrode 9 is applied to a method of corona transfer to a transfer paper 10 via a dielectric belt 11, 1) the transfer performance at high humidity described above is obtained. 2) The transfer paper 10 is electrostatically adsorbed to the dielectric belt 11 before it comes into contact with the photoconductor 12, and the transfer paper 10 is not adsorbed to the photoconductor 12 There is a new effect of improving the separation performance of.

In order to further improve the second effect of separating the paper from the photoconductor, as shown in FIG.
It has been found that it is effective to newly install a suction corona charger 14 inside this and apply a voltage 17 having a polarity opposite to the voltage 16 applied to the conductive electrode 15 to this corona charger 14. This is because the transfer paper 18 and the dielectric belt 13 come into contact with each other by being sandwiched between the conductive electrode 15 and the corona charger 14 to which the voltages of opposite polarities are applied, so that the electrostatic attraction between the paper 18 and the belt 13 is generated. Is extremely strong and the separation performance from the photoconductor 19 is improved.

Further, in the structure shown in FIG. 5, it has been found that the adhesion between the transfer paper 18 and the transfer belt 13 is improved, and a non-uniform air layer is removed between the transfer paper 18 and the transfer belt 13, so that a third effect is newly exhibited. . The third effect is that the transferability of toner is remarkably improved in a color electrophotographic apparatus of a system in which toner images of a plurality of colors are superposed on a photoconductor to form a color image and are collectively transferred to paper. In such an apparatus, the toner adhered on the photoconductor continues to be subjected to corona charging a plurality of times, so the toner on the photoconductor changes to a different charge amount depending on the order of development, and the optimum transfer condition is set for each toner. Different. In an extreme case, the first developed toner is not transferred under the condition where the first developed toner is transferred to the paper, and conversely, the first developed toner is first developed under the condition where the last developed toner is transferred. Development occurred in which toner was not transferred. Also in such a color electrophotographic apparatus, as shown in FIG. 5, the corona charger 14 is installed inside the dielectric belt 13, and the transfer paper 18 and the dielectric belt 13 are provided by the corona charger 14 and the conductive electrode 15. With the configuration in which and are sandwiched for transfer, transfer of all toner is improved under all environments.

Examples As an electrostatic image carrier used in the present invention, electrostatic recording paper,
There is an electrophotographic photoreceptor in which a photoconductive substance such as amorphous selenium, zinc oxide, or polyvinylcarbazole is formed on a conductive material such as amiminium.

The conductive electrode used in the present invention may be provided at any position on the upstream side or the downstream side of the transfer position where the toner developed on the electrostatic image carrier is corona-transferred onto the transfer paper. On the side, since an unfixed toner image has already been transferred and exists on the transfer paper, rubbing with a conductive member at this position results in disorder of the toner image. Therefore,
It is preferably provided on the upstream side of the corona transfer position.

Also, in order to prevent excess corona charge from transferring to the photoconductor side at high humidity and remove the corona charge from the transfer paper, the conductive member in contact with the transfer paper is supplied with a power supply that applies a voltage of the opposite polarity to the polarity of corona transfer. Need to connect. At this time, in the case of normal development, for example, the photoconductor becomes positive, the toner becomes negative, the corona transfer voltage becomes positive, and the voltage applied to the conductive electrode becomes negative. In the case of reversal development, for example, the photoconductor is positive, the toner is positive, the corona transfer voltage is negative, and the voltage applied to the conductive electrode is positive.

In order to absorb the electric charge uniformly from the paper, the conductive electrode is particularly effective when it is a conductive brush. Suitable materials for the conductive brush are stainless fiber, rayon fiber in which carbon black is dispersed, carbon fiber and the like.

It is also effective to use a conductive roller 20 as the conductive electrode as shown in FIG. At this time, since the roller 20 rotates, no resistance is generated when the transfer paper 21 passes between the dielectric belt 22 and the roller 20, and the paper conveyance property is excellent. Examples of the material of the roller 20 include a roller shape of the conductive fur brush and a conductive rubber roller.

The range of voltage applied to the conductive electrode is 100 to 2 kV, preferably 200 to 1 kV. At a voltage of 100 V or less, the excessive transfer corona is too little sucked in at high humidity, resulting in no effect.
Above V, the transfer corona is sucked too much, resulting in poor transfer.

When the transfer device is a device that sandwiches the transfer paper between the dielectric belt and the photoconductor and performs corona transfer from the back surface of the dielectric belt, not only the transfer paper at high humidity but also the resistance value of the dielectric belt is affected, The present invention is particularly effective in such a case because the transfer efficiency is further reduced. At this time, as the dielectric belt used for transfer, an insulating belt made of, for example, a fluoroethylene resin, a polyester resin, or glass fiber is used. Further, a belt having a structure in which a high resistance material layer such as polytetrafluoroethylene or polyethylene terephthalate is applied to the surface of rubber made conductive by dispersing carbon black or the like is used. If the conductive layer of this belt is made completely conductive, the transfer electric field will be blocked and transfer will not be possible. Therefore, it is desirable that the resistance value is in the range of 10 ⁴ to 10 ¹⁰ Ωcm. Further, the thickness of the transfer belt is preferably in the range of 200 μm to 2 mm.

If a corona charger that applies a voltage of the opposite polarity to the voltage applied to the conductive electrode is installed at the opposite position inside the belt via the dielectric belt of the conductive electrode, the transfer paper absorbs the charge from the conductive electrode. Can be performed more positively, and since a large electric field is applied between the transfer paper and the dielectric belt, the adhesion between the transfer paper and the dielectric belt increases, and the photoconductor and transfer paper come into contact during transfer. The effect that the paper is not electrostatically adsorbed by the photoconductor and the separability between the photoconductor and the transfer paper is improved.

Further, for example, as shown in Japanese Patent Application No. Sho 60-212927, the image recording method repeats the charging, exposing and developing steps using toners of a plurality of colors to form a color image on the photoconductor, and then the color image is formed on paper. In the image recording method of transferring, since the toner is developed on the photoconductor and the corona charging is further repeated on the toner, toner having various charge amounts is mixed on the photoconductor. It is difficult to uniformly transfer such a color image under the same conditions by the conventional corona transfer method, but it is extremely easy to use the transfer device having the configuration of the conductive electrode to which the voltage is applied and the dielectric belt according to the present invention. become.

The toner to be transferred is described as a dry toner here, but the same effect can be obtained by using a wet toner.

Hereinafter, specific examples of the present invention will be described in more detail.

Example 1 A color image was formed using the apparatus shown in FIG.

The transfer belt 23 has a structure in which the surface of a conductive rubber belt in which carbon black is dispersed is coated with Teflon, and has a resistance value of 10 ⁸ Ωcm and a thickness of 1 mm. The developing devices 24, 25 and 26 are non-contact type non-magnetic one-component developing devices that fly the toner by a DC electric field, and the toner is triboelectrically charged by the conductive fur brushes 27, 28 and 29 which are in contact with the developing roller,
On the aluminum developing rollers 30, 31, 32, the blade
33, 34 and 35 form a thin layer of toner. The developing device 24 contains yellow (Y), the developing device 25 contains magenta (M), and the developing device 26 contains cyan (C) insulating toner. The black developing device 36 is a contact-type developing device containing a two-component developer consisting of an insulating toner and a magnetic carrier, which is widely used in electrophotographic devices. And developing roller 3
Each developing unit was installed around the photoconductor 38 so as to face each other with a constant gap (development gap) between 0, 31, 32, 37 and the photoconductor 38. Each developing device is provided with a separating / contacting mechanism that is close to the photoconductor 38 during development and separated during non-development.

The specifications and developing conditions of the black developing device 36 and the physical properties of the toner are shown below.

Specifications of developing device and developing conditions Diameter of developing roller 37: 22 mm Peripheral speed of developing roller 37: 320 mm / s Developer layer thickness on developing roller 37: 400 μm Rotation direction of developing roller 37: Opposite to photoconductor 38 ( Same direction) Development gap (gap between the surface of the developing roller and the surface of the photoconductor): 300μ during development, 2mm during non-development Physical properties of developer: Two-component developer of toner and carrier Average particle size of carrier: Approx. 50 μm Carrier type: Teflon coated ferrite Toner charge: 15 μC / g Toner average particle size: 12 μm Toner dielectric constant: Approx. 2 Yellow, magenta and cyan developing device specifications and developing conditions, and toner physical properties are shown below. .

Development device specifications and development conditions Development roller diameter: 20 mm Development roller peripheral speed: 160 mm / s Development roller rotation direction: Opposite direction to photoconductor 38 (same direction) Toner layer thickness on development roller: 30 μm Development Gap (gap between the surface of the developing roller and the surface of the photoconductor): 150 μm at development, 2 mm at non-development Physical properties of toner Toner charge amount: +3 μC / g Average particle size: 12 μm Dielectric constant: about 2 Infrared region as a photoconductor Long-wavelength sensitized amorphous Se-Te photoconductor drum 38 with a diameter of 152.8 mm (photosensitive layer thickness of 63 μm, relative dielectric constant of about 7, long-wavelength-sensitized function-separated selenium photoconductor, at wavelength of 790 nm A half-exposure amount of 0.6 μJ / cm ² ) was used, and rotation was performed at a peripheral speed of 160 mm / s. The photoconductor 38 was charged to a charging potential of + 900V by a charger 39 (Scoroton charger, corona voltage: + 7kV, grid voltage: 1kV). Next, the semiconductor laser 40 having a wavelength of 790 nm was emitted and exposed.
At this time, the light intensity on the photoconductor surface was set to 1.5 mW. Using this semiconductor laser 40, a negative black signal was exposed on the photoconductor 38 to form an electrostatic latent image. The latent image on the developing roller
After applying + 600V to 37, the black developing device 36 in the developing state reversely develops it to form a black toner image, and then the photoconductor 38 is once charged with an AC corona charger 41 (applied AC voltage: 4.5 kVr ms, DC bias component; Removed electricity at + 200V. The thickness of the black toner layer developed on the photoconductor 38 was 1 to 2 layers, and the thickness of the toner layer was 10 to 20 μm.

Next, the photoconductor 38 was charged to + 600V again by the corona charger 39 (scorotron charger, corona voltage: +7 kV, grid voltage: +600 V). At this time, the charging potential of the photoconductor 38 to which the black toner adhered becomes + 600V. After that, photoconductor 38
Then, the electrostatic latent image of yellow is formed by exposing the signal light corresponding to yellow by the semiconductor laser 40. Here, the exposure amount of the semiconductor laser was set to 1.5 mV on the surface of the photoconductor. Next, by applying + 600V to the developing roller 30 of this photosensitive member, a yellow developing device 24 in a developing state and a magenta developing device 25 in a non-developing state,
A yellow toner image was formed by passing the toner through a cyan developing device 26 and a black developing device 36. Next, this photoconductor 38 is neutralized by an AC corona charger 41 (applied AC voltage; 4.5 kVrms, DC bias component: +200 V), and again the corona charger 39 (scorotron charger, corona voltage: +7 kV, grid voltage: +940
V) charged the photoconductor 38 to + 810V. At this time,
The charging potential of the photoconductor 38 with the black and yellow toner attached was + 840V. Then, the semiconductor laser 40 exposed the signal light corresponding to magenta to form a magenta electrostatic latent image. Next, the photoconductor 38 is undeveloped in the yellow developing device 24,
The developing roller 31 was passed through a magenta developing device 25 in a developing state in which +800 V was applied, and a magenta toner image was formed. At this time, the toner layer in the portion where the yellow and magenta overlap on the photoconductor 38 is 2 to 4 layers, and the thickness thereof is 20 to 40 μm.
It was m. After that, the photoconductor 38 was passed through the non-developed cyan developing device 26 and black developing device 36.

Next, the photoconductor 38 is charged with an AC corona charger 41 (applied AC voltage;
The charge was removed with 4.5 kVrms, DC bias component; +200 V), and the photoconductor 38 was again charged with +850 V by the corona charger 39. At this time, the charging potential of the photoconductor 38 to which only the black, yellow, and magenta toners were attached became + 870V. Further, the charging potential of the photoconductor 38 in the portion where the yellow and magenta toners overlap each other becomes + 780V. After that, the semiconductor laser 40 exposed signal light corresponding to cyan to form a cyan electrostatic latent image. Next, the photoconductor 38 is applied to the non-developed yellow developing device 24, the magenta developing device 25, and the developing roller 32 by + 830V.
Then, the toner is passed through a developing cyan developing device 36 to form a cyan toner image, and a color image is completed on the photoconductor 38.

The plain paper 42 is conveyed on the dielectric belt 23 while being in contact with the stainless steel fur brush 43 to which a voltage of +1 kV is applied, and is passed between the paper adsorption charger 44 (applied voltage; -6 kV) to It was attached to the body belt 23. The color toner image obtained on the photoconductor 38 is transferred onto the paper 42 by the transfer charger 45 (applied voltage; −6 kV), and then the paper separation charger 46.
After the paper is charged by (applied voltage; -6kV), the paper is separated from the dielectric belt 23, and the positive charger 47 (applied voltage; + 6kV)
V) and a negative charger 48 (applied voltage; −6 kV) are passed between a pair of chargers for charging, and the fixing device 49 performs heat fixing.

On the other hand, after the transfer, the surface of the photoconductor 38 is
(Applied AC voltage: 4.5 kVr ms, DC bias component: +800
V) was exposed to corona and the photoconductor was decharged. After that, −350V
Conductive fur brush cleaner with applied voltage of 50 (resistivity of carbon black dispersed in rayon fiber 10 ⁵ Ωcm
(A fur wrapped around a stainless steel rod)
It was pressed against 38 and cleaned.

As a result, hygroscopic paper (hygroscopic
(14%), all the toners of black, yellow, magenta, and cyan were completely transferred to the paper, and a clear image was obtained.
In addition, transfer failure did not occur even in a dry state at 10 ° C and 15% relative humidity. Further, a paper transport test of 10,000 sheets was carried out in a high humidity environment, but no separation failure in which the paper was wrapped around the photoconductor did not occur.

Example 2 An experiment was conducted using the electrophotographic apparatus shown in FIG. Photoconductor 51
An organic photoconductor in which an azo pigment is dispersed in a polyester resin was used, and it was rotated at a speed of 100 mm / s in the direction of the arrow and charged to −800 V by a corona charger 52. Next, the reflected light of the original was exposed at the exposure position and further developed by a two-component magnetic brush developing device 53 containing toner charged to +10 μC / g.

Next, the transfer paper 54 is conveyed to the transfer position below the photosensitive drum 51 while contacting the conductive fur brush 55 to which a voltage of + 500V is applied, and the transfer corona at the transfer position to which the negative voltage is applied is applied. The toner image developed on the photoconductor 51 is transferred onto the transfer paper 54 by the 56.

As a result, hygroscopic paper (hygroscopic
(14%), the toner was completely transferred to the paper and a clear image was obtained. In addition, no transfer failure occurred even when dried at 10 ° C and 10% relative humidity.

Example 3 Next, an experiment was conducted using the apparatus shown in FIG.

Amorphous selenium photoconductor is used for photoconductor 57, and
It rotated at a speed of 0 mm / s and was charged to +800 V by the charger 58.
Next, the reflected light of the original is exposed at the exposure position, and-
It was developed by a two-component magnetic brush developer 59 containing toner charged to 10 μC / g.

In the apparatus shown in FIG. 8, an insulating belt 60 made of polyester resin is arranged in the transfer portion so as to contact the photosensitive drum 57. The transfer paper 61 is conveyed to the transfer position of the photosensitive drum 57 by this belt 60. The transfer paper 61 is attracted onto the transfer belt 60 by bringing it into contact with the conductive fur brush 62 to which a voltage of -700 V is applied, and by the transfer corona 63 provided with a positive voltage provided below the photosensitive drum 57, The toner image developed on the photoconductor 57 was transferred onto the transfer paper 61.

As a result, hygroscopic paper (hygroscopic
(14%), the toner was completely transferred to the paper and a clear image was obtained. In addition, no transfer failure occurred even when dried at 10 ° C and 10% relative humidity.

EFFECTS OF THE INVENTION According to the present invention, in an apparatus for corona-transferring a toner image recorded on an electrostatic image carrier, a toner transfer that can always stably and favorably transfer regardless of the degree of moisture absorption of paper. The device can be obtained.

[Brief description of drawings]

FIG. 1 is a side view of a color electrophotographic apparatus using a toner transfer device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a main part for explaining problems of a transfer device of a conventional example, and FIG. FIG. 4, FIG. 5, FIG. 6 and FIG. 6 are schematic views of a toner transfer device according to another embodiment of the present invention, and FIGS. 7 and 8 show the toner transfer device according to the embodiment of the present invention. It is a side view of the electrophotographic apparatus which used another Example. 23 ... Dielectric belt, 24 ... Yellow developing device, 25 ... Magenta developing device, 26 ... Cyan developing device, 36 ... Black developing device, 38 ... Photoconductor,
39 ... Corona charger, 40 ... Semiconductor laser, 43 ... Conductive fur brush, 44 ... Adsorption corona charger, 45 ... Transfer charger, 52
… Thermal fuser.

Claims (1)

[Claims] 1. A toner transfer for use in a color electrophotographic apparatus, wherein a plurality of color toners are used to repeat a charging / exposure / reverse development process to form a color toner image on a photoconductor, and then a corona transfer is collectively performed on paper. An apparatus, comprising: a dielectric belt configured to carry and convey the paper on a surface thereof, and to transfer the toner image by bringing the paper into contact with the photoconductor between the photoconductor and the corona transfer device; , A voltage having a polarity opposite to that of the corona transfer device, which contacts the paper at a position upstream of the photoconductor contact position in the traveling direction and at a position away from the photoconductor contact position by a distance shorter than the length of the paper. A toner transfer device having a conductive electrode to which is applied.